e.g. Alt+X is a shortcut key in configuration A only.
Select multiple configurations (including A) and open their Keyboard properties.
Press Alt+X in “Press New Shortcut Key” field.
** “Currently Assigned to” shows “[Undefined]”.
Suggestion:
“Currently Assigned to” should show “[*]” or something.
Also, should show some symbol in “Current Keys” list in such cases.